A wing is an important part of an airplane for providing a lift force to the airplane. During the flight of the airplane, both an upper surface and a lower surface of the wing can generate a lift force, and the upper surface is the main lift force surface. In order to maintain the efficiency of generating lift force of the wing, disturbance to the upper surface of the wing should be avoided as much as possible. In the wing-mounted arrangement, the suspension is a part connecting an engine and the wing. A fairing aerodynamic surface of the suspension is a directly visible part exposed outside of the suspension. As shown in FIGS. 1-2, the fairing aerodynamic surface G′ of the suspension 20 generally extends from a start point P close to a leading edge of an engine nacelle 10 towards the rear part of the airplane in the airflow direction, and has an inner side surface and an outer side surface. A rear part of the fairing aerodynamic surface G′ at the lower surface 32 of the wing and close to a trailing edge of the wing 30 shrinks to be a line or a surface with a relative small width. As for the airplane with a wing-mounted arrangement, the main difficulty of mounting the engine to the wing in a close range lies in the arrangement of the suspension having certain inner space. In the prior art as shown in FIGS. 1 and 2, the fairing aerodynamic surface G′ of the suspension extends rewards to the upper surface of the wing at a substantially the same maximum height Hmax after rising to the maximum height position, that is to say, an intersecting point O′ between the fairing aerodynamic surface G′ and the leading edge 31 of the wing is located on the upper surface of the wing, which will cause disturbance to the wing 30, specifically the upper surface of the wing, thereby reducing the lift force of the airplane and decreasing the performance of the airplane. Thus, the disturbance to the upper surface of the wing needs to be reduced if the engine is desired to be mounted to the wing in a close range.
For facilitating the description, the fairing aerodynamic surface of the suspension will be abbreviated to “suspension” in the following description.
The suspension comprises structures needed by suspending the engine of the airplane, and inner systems, electrical cables, seals and structure members that are necessary for maintaining the operation of the engine and the airplane, and these components has a certain requirements for the inner space of the suspension. In order to ensure the inner space of the suspension, the following solutions are generally utilized.
1. The distance between the engine and the leading edge of the wing is increased, so that the inner space of the suspension is increased, and thus the suspension is kept under the leading edge of the wing.
2. The suspension has a relative large height and extends rearwards to a position above the leading edge of the wing, that is to say, the suspension extends to the upper surface of the wing.
3. The suspension is kept below the leading edge of the wing, but the width of the suspension needs to be increased.
These solutions have both advantages and disadvantages. In the first solution, the length of the landing gear is increased since the distance between the engine and the leading edge of the wing is increased, which will increase the weight and the fuel consumption of the airplane, reduce the payload of the airplane and affect the carrying capacity of the airplane. In the second solution, the height of the landing gear is not increased, thus the disadvantageous influence in the first solution can be avoided, but the flight performance of the airplane is reduced. That is to say, when the suspension extends rearwards to the position above the wing, the suspension will cause a flow separation on the upper surface of the wing in the case of small angle of attack so that the drag force is increased, or causes a flow separation at a large area on the upper surface of the wing in the case of large angle of attack so that the pitching up of the moment happens in advance, which will endanger the safety of the airplane, thus the second solution has a significant influence on the upper surface of the wing. In the third solution, the disadvantages influence caused by increasing the length of the landing gear in the first solution and the disturbance to the upper surface of the wing in the second solution can be avoided, but increasing the width of the suspension can reduce the area of the cross section of the flow-out channel of the engine, which will block the flowing in the engine and reduce the engine thrust, thereby reducing the propulsive efficiency of the engine.
In order to eliminate or reduce the disadvantageous influence caused by the suspension extending to the position above the wing, W08401347A1 discloses that an auxiliary device is arranged close to the fairing of the suspension, which can reduce the disadvantageous influence on the lift characteristic of the airplane due to the suspension extending to the position above the wing by inducing impact wave on the upper surface of the wing. U.S. Pat. No. 3,960,345 discloses that a fin is provided to the nacelle surface of the wing, which can suppress the vortex caused by the engine or the suspension extending to the position above the wing, increase the lift force and drag force of the airplane, enhance the stability, and reduce the disadvantageous influence on the airplane due to the downwash. U.S. Pat. No. 3,968,946A discloses that a movable fairing is provided to fill the gap between the fixed fairing and the leading edge slat when the engine or the suspension extends to the upper surface of the wing. The above solutions disclosed in the above patents overcome the disadvantageous influences due to the suspension extending to the position above the wing by adding an additional device, which may increase the additional weight of the airplane, reduce the airplane payload, and reduce the carrying performance of the airplane.